The objectives of this project are to define and generate filarial and strongyloides proteins that are important in inducing parasite-specific immune responses in the human host and to understand, at a molecular level, the differences among related helminth species. Recombinant antigens and probes have been identified that a) encode immunoreactive and potentially protective molecules of W. bancrofti; b) can distinguish among related filarial species; c) identify repeated segments of the W. bancrofti, O. volvulus and Loa loa genome; d) are of potential diagnostic importance; and e) are responsible for the induction of immediate hypersensitivity type responses in filarial infections. Further, cDNA libraries of filariform and rhabdiform larvae of S. stercoralis have been made and characterized and phylogenetic trees have been constructed for this parasite using 5S ribosomal sequences.